It is known to use metal oxides as cathode materials in nonaqueous electrochemical cells. For example, U.S. Pat. No. 4,310,609 to Liang et al. and U.S. Pat. No. 5,670,276 to Takeuchi at al., which are assigned to the assignee of the present invention and incorporated herein by reference, disclose a metal oxide composite cathode comprising metals and metal oxides. The Liang cathode is prepared from readily decomposable precursor compounds, including nitrates of vanadium, silver and copper, decomposed in a combined state, or individually decomposed and thereafter combined in an oxide/decomposable metal salt compound and subsequently decomposed to form the metal oxide composite cathode. More specifically, the preferred cathode composites are prepared by decomposing a vanadium salt, suitably ammonium metavanadate, to produce vanadium pentoxide. A decomposable metal salt, suitably the nitrate of a second metal is then added to the vanadium pentoxide. The second metal is preferably selected from the group consisting of silver, copper, manganese and mixtures thereof. The resultant composite cathode material includes V2Ox wherein x≦5 combined with one or more of Ag2Oy wherein y=0 to 1; CuOz wherein z=0 to 1; and MnOk wherein k=1 to 3. The composite material is described as a metal oxide-metal oxide, a metal-metal oxide, or a metal-metal oxide-metal oxide. A preferred embodiment of this cathode material has the formula AgV2O5.5, also referred to as SVO.
The Liang et al. patent does not specifically disclose combining vanadium pentoxide with silver and copper as a preparation for the trimetallic compound copper-silver vanadium oxide. In that light, Liang et al. does not specifically disclose a mixture of vanadium pentoxide combined with copper nitrate and silver oxide or copper oxide and silver nitrate, such as is disclosed by the present invention.
The Takeuchi patent discloses a copper silver vanadium oxide (CSVO) having a formulation of CuxAgyV2Oz that is preferably about 0.01≦x≦1.0, about 0.01≦y≦1.0 and about 5.01≦z≦6.5. The applicants have found that the Takeuchi cathode material is not a crystallographic phase pure formulation. The applicants have discovered that the active cathode formulation disclosed by Takeuchi contains multiple crystallographic phases which tend to affect an electrochemical cell's electrical performance when the material is utilized as an electrochemical cell cathode.
Specifically, the applicants have discovered that the multiple phases that are contained within the Takeuchi CSVO active cathode material have a tendency to increase internal electrical resistance within a cell. As a result, the overall energy capacity of an electrochemical cell constructed with a cathode composed of the Takeuchi CSVO material is generally less than that of an electrochemical cell constructed with a cathode composed of the phase pure copper silver vanadium oxide material of the present invention. In addition, the presence of the multiple phases within the Takeuchi active cathode material generally hinder consistent and reproducible material manufacture. Because the formation of these crystallographic phases require very specific manufacturing conditions, the ability to exactly replicate the amount and growth of these multiple crystallographic phases is difficult to achieve.
The present application therefore, discloses a more preferred crystallographic phase pure copper silver vanadium oxide (CSVO) material having the general formula CuxAgyV4Oz, where x=0.01 to 4, y=0.01 to 4 and z=7.01 to 13.5 and that may be used to produce cathodes for electrochemical cells. The active cathode CSVO material formulation is more manufacturability robust and its electrical properties are less dependent on varying manufacturing conditions. In addition, the phase pure CSVO active cathode material formulation of the present invention provides electrochemical cells having improved energy capacity.